The Oil & Gas sector represents one of MEILONG TUBE principal marketsfor supply of a wide range of tubular product forms and materials. Ourproducts have been successfully used in some of the most aggressivesubsea and downhole conditions and we have a long proven trackrecord of supplying products that meet the strict quality requirements ofthe Oil & Gas and geothermal energy sectors.

Improvements in the technology for the enhanced exploitation of oil andgas fields has increasingly required the use of long continuous lengths ofstainless steel and nickel alloy tubulars for hydraulic control, instrumentation,chemical injection, umbilical and flowline control applications. Thebenefits of this tubular technology have resulted in reduced operatingcosts, improved recovery methods and reduced capital expenditure byconnecting downhole valves and chemical injection with remote andsatellite wells to a fixed or floating central operating platform.

Manufacturing Range

Coiled tubing is available in a range of different product forms dependingon the customer requirements. We manufacture seam welded andredrawn, seam welded and floating plug redrawn and seamless tubeproducts. The standard grades are 316L, alloy 825 and alloy 625. Othergrades of stainless steel in duplex and superduplex and nickel alloy areavailable on request. Tubing can be supplied in the annealed or coldworked condition.

MEILONG offers coiled control line in stainless steel and nickel alloys.Our products are used in the following applications:• Downhole hydraulic control lines.• Downhole chemical control lines.• Subsea control lines for hydraulic power and chemical injection.• Smoothbore control lines used in fibre optic applications.

Quality Considerations

When specifying the type of tubing for a particular environmentseveral factors should be taken into account. The most importantcriteria influencing this decision will be pressure capability and risk ofcorrosion. A seamless tube that has been cold worked and annealedhas a completely homogeneous crystalline wrought structure. Thestrip material used to make a welded tube is of the same form butthis becomes a cast structure at the weld, which could corrodepreferentially to the surrounding tube. Through the combination of coldwork and subsequent annealing the weld metal can be re-crystallised,transforming this area to a wrought structure resulting in a homogeneouscross-section with equal corrosion potential all around the tube similarto a seamless tube. Sinking goes a long way to achieving this recrystallisationof the cast weld structure into a partially homogenisedannealed structure. The extra work in the weld area imparted by passes of drawing processes ensure full re-crystallisation.

In theory the pressure capability of tubing made by the welded andannealed method should be the same but it is common practice indesign codes to down-rate welded tubing due to the risk of an imperfectweld leading to weakness. The strains involved in a following redrawingoperation will establish the quality of the seam weld and any centre-lineweakness will be exposed and detected by visual inspection and/orpressure testing. Therefore the seamless welded and sunk and welded &sunk/plug drawn tubes have the same pressure rating which is superiorto that of welded tubing.

Other considerations that can affect the type of tubing specified aresurface roughness, compatibility with compression fittings, tolerances,concentricity, length and, of course, price. Welded tubing has a smoothOD & ID finish except for the bead, which can be pronounced in theweld area. This can cause problems with compression fittings. Welded& sunk tubing has a smooth OD surface making it suitable for use withcompression fittings but a somewhat rougher bore condition due tosinking and a pronounced weld bead on the ID only. Welded & plugdrawn and seamless tubes have a smooth OD surface together with auniform bore surface with no protruding weld bead.

Tubes made by welding from strip are generally more concentric thanseamless tubes, where the uniformity of wall thickness is dependenton the concentricity of the first piercing into hollow form. However,seamless tubes will meet standard commercial tolerances such as thosein ASTM A269.

Generally longer lengths can be made by seam welding from strip thancan be obtained by drawing down from seamless hollows. These lengthscan be further extended by sinking or plug drawing. Where very longlengths are required individual coils can be butt welded together usingautogeneous orbital welding, each weld being radiographically examinedto ensure that it is free of defects and the complete line is then subjectto a pressure test. Welded and redrawn type tubing will need far fewerjoints than a seamless line of the same overall length, which leads tosignificant cost savings.

Advantages of Redrawing Welded Tube

Long lengths can be made by seam welding formed strip but suchtubing has OD & ID discontinuity and may suffer from local problems ofmechanical strength or corrosion. A welded & sunk tube improves theseaspects and has been proven reliable in service over several decades foroffshore applications. Although more expensive than welded only tubing,the welded and redrawn tube is still relatively inexpensive compared toSeamless.

Seamless tubing has cross sectional uniformity however, it is the mostexpensive method of manufacture and has a limitation in the continuouslength that can be produced between joints. For a slight premium overthe welded & sunk price, tubing can be produced by the welded & floatingplug drawn process which results in a product of similar appearanceto seamless but with the significant advantage of much longer continuouslengths and greatly reduced costs.

Quality Assurance

Process and quality control of MEILONG TUBE products is critical in respectof consistently achieving the highest standards in critical Oil & Gasapplications. Strict quality control is applied at every stage of the processingoperations. Individual quality plans tailored to the customers'project requirements can also be incorporated into our product quality.

The control line is 100% dimensionally inspected and eddy current testedto international ASTM or DIN standards. All lines are 100% hydraulicallypressure tested before being released and certified. Any orbital jointsare also radiographically tested in a minimum of 3 planes to ensure thequality of the joint.

The working pressure for a tube depends on the operating conditionsof each particular application and the factor of safety required. This canbe determined only by the customer and is expressed as a proportion ofeither the yield pressure or the nominal burst pressure of the tubing.These are the values that raise the stress to the theoretical yield point orthe ultimate tensile strength for the material.

Safe working pressures have traditionally been expressed as aproportion of either the tensile strength or yield point of a tube. Differentindustries and pressure vessel codes have adopted different practices.

Quality assurance

The quality of our products for the control line in oil and gas sector is assurednot just during the controlled manufacturing process but also byway of finished product testing. Typical tests include:• Non-destructive tests• Hydrostatic tests• Surface finish controls• Dimensional accuracy measurements• Flare and coning tests• Mechanical and chemical property testing